In studying the activity of glyceraldehyde phosphate dehydrogenase and phosphoglycerate kinase in erythrocyte membranes we hope to accomplish the following objectives: 1. to see if GPDH and PGK can be reversibly dissociated from and reassociated with the membrane and to determine the conditions which affect their association and dissociation; 2. to determine the specificity of interaction of these proteins with the membrane fractions using chemical modification of the proteins and natural variants of these enzymes; and 3. to determine how interaction of GPDH and PGK wth the membrane affects their enzymatic activities by comparing the kinetic constants and sensitivity to cations of the membrane-bound and soluble forms of the enzymes.